Reactions of N-heterocyclic ligands with substitutionally labile organometallic complexes, [(η5-C5R5)Fe(CO) 2E]BF4

Article abstract of DOI:10.1016/j.ica.2012.04.003

The ether complexes [Cp(CO)₂Fe(OEt₂)]BF₄ (Cp = η⁵-C₅H₅) (1) and [Cp(CO) ₂Fe(THF)]BF₄ (Cp = η⁵-C₅(CH ₃)₅) (2) react with 1,3

Full text of DOI:10.1016/j.ica.2012.04.003

Inorganica Chimica Acta 390 (2012) 83–94
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Reactions of N-heterocyclic ligands with substitutionally labile organometallic
complexes, [(g
5-C5R5)Fe(CO)2E]BF4
b
a
Cyprian M. M’thiruaine a, Holger B. Friedrich a, , Evans O. Changamu , Muhammad D. Bala
⇑
a School of Chemistry, University of KwaZulu-Natal, Private Bag X54001, Durban 4000, South Africa
b Chemistry Department, Kenyatta University, P.O. Box 43844, Nairobi, Kenya
a r t i c l e i n f o
a b s t r a c t
Article history:
The ether complexes [Cp(CO)2Fe(OEt2)]BF4 (Cp =
g
5-C5H5) (1) and [Cp⁄(CO)2Fe(THF)]BF4 (Cp⁄ = g5
-
Received 21 October 2011
Received in revised form 29 March 2012
Accepted 1 April 2012
C5(CH3)5) (2) react with 1,3,5,7-tetraazaadamantane (HMTA) to give stable water-soluble dinuclear
complexes [{( -HMTA)](BF4)2 (R = H; R = CH3) and mononuclear complexes [(
5-C5R5)(CO)2Fe}2( 5-C5R5)
(CO)2Fe(HMTA)]BF4 (R = H; R = CH3). The reaction of 1 with 1,4-diazabicyclo[2.2.2]octane (DABCO) gave
good yields of the dinuclear and mononuclear complexes, [{Cp(CO)2Fe}2( -DABCO)](BF4)2 (6a) and
g
l
g
Available online 7 April 2012
l
[Cp(CO)2Fe(DABCO)]BF4 (6b), respectively, depending on reagent ratios. Similar reactions with 2 gave very
low yields of the mononuclear complex [Cp⁄(CO)2Fe(DABCO)]BF4 (6c) as the only product. The reactions of
[Cp(CO)2Fe(HMTA)]BF4 (3b) and [Cp⁄(CO)2Fe(HMTA)]BF4 (4b) with NaBPh4 in acetone proceeded
Keywords:
N-heterocyclic iron complexes
1-Methylimidazole
1,3,5,7-Tetraazaadamantane
1,4-Diazabicyclo[2.2.2]octane
-
smoothly at room temperature to give the corresponding BPh4 salts. Reaction of 4b with 1 at room
temperature gave the dinuclear complex [{Cp(CO)2Fe}2(
the same reaction conducted at 0 °C led to the unstable mixed ligand complex [{Cp(CO)2Fe}(
{Fe(CO)2Cp⁄}](BF4)2. The reactions of 1 and 2 with 1-methylimidazole (1-meIm) gave high yields of
[(
5-C5R5)(CO)2Fe(1-meIm)]BF4 (R = H (7); R = CH3 (8)), of which the NMR, IR and single crystal X-ray
l
-HMTA)](BF4)2 (3a) as the major product, while
l
-HMTA)
g
studies reveal the coordination of 1-methylimidazole to be via the ‘pyridine nitrogen’ of the imidazole
ring. Single-crystal X-ray diffraction studies reveal that compounds 3a and 8 crystallize in the orthorhom-
bic P212121 and Pna21 space groups, respectively. Compound 7 however, crystallized in the monoclinic
P21/c space group with three independent molecular cations and anions each in the asymmetric unit.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
activity has been the subject of many patents in recent years. For
example, methenamine (HMTA), methenamine anhydromethyl-
In recent years, there has been a great deal of interest in com-
plexes bearing cage-like 1,3,5-triaza-7-phosphaadamantane (PTA)
[1–6] due to its ability to solubilize metal complexes in the aque-
ous phase [7,8]. Some of these complexes have found application
in aqueous phase and biphasic catalytic systems [9–13] as well
as in pharmaceuticals [5,7]. The synthesis of water-soluble organo-
metallic derivatives has been widely achieved by the design of
water-soluble ligands that, when incorporated into the coordina-
tion sphere of the metal, impart water-solubility to the complexes.
The solubilizing ability of the PTA complexes for instance is im-
parted by the nitrogen atoms which form hydrogen bonds with
water molecules.
PTA and other N-based aromatic heterocycles have also been
widely used as metal coordination spacers owing to their good do-
nor ability and rigidity [14–16]. HMTA and its derivatives, in partic-
ular, have been used as antibacterial agents in the treatment of
urinary tract infections since 1932 [17–19], and their anti-bacterial
ene-citrate, methenamine hippurate, methenamine mandelate
and methenamine sulfosalicylate have all been reported as syn-
thetic antibacterials [20] and as anti-infectives [21]. HMTA has also
been applied in the treatment of ear canal infections in combination
with anti-inflammatory and antiseptic agents [22], and as an adju-
vant to radiation and cisplatin in the treatment of solid tumors [23].
In recent years HMTA has been used as base catalyst in the synthe-
9
i
sis of phenolic gel and most recently Garc
a et al. published a report
on the use of HMTA as a base catalyst to control the porosity and
pore size of resorcinol furaldehyde cryogels synthesized in t-buta-
nol [24].
DABCO is known mainly as an organic catalyst in a large variety
of organic syntheses [25–27]. For example it has displayed high
catalytic activity in the methylation of indole in conjunction with
dimethyl carbonate [28]. Gordon et al. have demonstrated that
DABCO derivatives can also be used as Voltage-Gated potassium
channel blockers [29]. To the best of our knowledge, the DABCO
iron complexes of the type [(CO)4Fe(DABCO)] and [{(CO)4Fe}2(l-
DABCO)] are the only reported iron carbonyl complexes incorporat-
ing the DABCO ligand in the coordination sphere [30].
⇑
Corresponding author. Tel.: +27 312603107; fax: +27 312603109.
E-mail address: friedric@ukzn.ac.za (H.B. Friedrich).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.04.003

84
C.M. M’thiruaine et al. / Inorganica Chimica Acta 390 (2012) 83–94
1-Methylimidazole (1-meIm) is a derivative of imidazole (Im)
(Sections 4.2–4.12) as well as single crystal X-ray diffraction. Mass
spectroscopy data of compounds 3a, 4b, 6b and 8 have also been
recorded in 100% water.
which also finds application in drug design [31,32] and catalysis
[32,33]. This has instigated interest in coordination of imidazole-
based ligands to transition metals [34] leading to the reporting of
a wide variety of imidazole transition metal complexes [35,36].
This includes the complexes [Cp(CO)2FeL-BPh3] (L = imidazole,
benzimidazole) reported by Nesmayanov et al. as a product of
2.1. Reaction of hexamethylenetetramine (HMTA) with the ether
complexes [(g
5-C5R5)(CO)2Fe(E)]BF4 (R = H, E = Et2O (1), R = CH3,
E = THF (2))
the decomposition reaction of the salts [Cp(CO)2FeLH]+ BPh4
-
[35]. A ligand substitution reaction could be an alternative route
to the cationic complex [Cp(CO)2FeL]+, whereby labile ligands such
as THF, Et2O or acetone are replaced by the imidazole ligand. How-
ever, such reactions have not been previously reported.
1,3,5,7-Tetraazaadamantane (commonly known as hexamethy-
lenetetramine and abbreviated HMTA), readily reacts with 1 at
room temperature to give the dinuclear complex 3a and the mono-
nuclear complex 3b. Similarly, the reaction of HMTA with 2 yields
the dinuclear complex 4a and the mononuclear complex 4b
whether the dinuclear or the mononuclear complex is isolated de-
pends on the stoichiometric ratio of the reagents employed. Thus,
the reaction of the etherate complexes with a slight excess of
HMTA furnished only the mononuclear product, while 1:1 or
2:1 mol ratios (etherate complex to HMTA) gave mixtures of dinu-
The importance of N-heterocyclic ligands in physiology, phar-
maceuticals and catalysis, as well as interest in exploration of the
coordination chemistry of amine ligands, aroused our interest in
the coordination of such ligands to transition metal centres of
varying electronic and steric environments. This may enhance an
understanding of their interactions with a metal ion and, hence,
provide models for active anti-bacterials or catalysts. For this re-
port, iron was the metal of choice since it is relatively non-toxic,
inexpensive and easy to handle due to the high stability exhibited
by its complexes. Moreover, iron complexes with bidentate N,N-li-
gands and tridentate N,N,N-ligands have been shown to catalyse
ethylene oligomerization and polymerization reactions [37–40].
Iron is also found in the blood of both vertebrates and inverte-
brates in which it forms Fe–N bonds in the heme group of hemoglo-
bin or myoglobin. To the best of our knowledge HMTA, DABCO and
clear [{(g l -
5-C5R5)(CO)2Fe}2( -HMTA)](BF4)2 and mononuclear [(g5
C5R5)(CO)2Fe(HMTA)]BF4 (R = H, CH3) complexes as products with
the relative amount of the mononuclear product decreasing with
increase in etherate reactant used in the reaction. When the mole
ratio of the reaction is raised to 4:1, only the dinuclear complex
[{(
for the formation of the tetranuclear complex [{(
Fe}4( 4-HMTA)](BF4)4 was obtained, even when large excesses of
the etherate complexes were employed. This is probably due to
the steric hindrance induced by the two {(
5-C5R5)(CO)2Fe} groups
g
5-C5R5)(CO)2Fe}2(
l
-HMTA)](BF4)2 was isolated. No evidence
g
5-C5R5)(CO)2-
l
1-meIm complexes with the {(
known. Herein, we report the syntheses and characterization of
the novel complexes of the types, [{(
5-C5R5)(CO)2Fe}2L)](BF4)2
and [(
5-C5R5)(CO)2FeL]BF4 (R = H, CH3; L = HMTA, DABCO) as well
as [(
5-C5R5)(CO)2Fe(1-meIm)]BF4 (R = H, CH3; 1-meIm = 1-meth-
g
5-C5R5)(CO)2Fe} moiety are un-
g
occupying two of four binding sites of the HMTA ligand.
g
The mononuclear complexes were obtained as yellow, while the
dinuclear complexes were obtained as orange solids. All the com-
plexes were soluble in water, acetone and acetonitrile. The com-
plexes 4a and 4b were also soluble in dichloromethane and were
easily isolated from solution by precipitation using diethyl ether.
It was difficult to separate the dinuclear from the mononuclear
compounds, thus pure samples of the dinuclear and mononuclear
compounds were obtained by using the appropriate mole ratios
of the reactants.
The IR spectra of compounds 3a–4b show two strong
absorption bands in the range 2058–1982 cmꢀ1 assignable to the
two terminal carbonyls as expected for cationic amine complexes
[44,48–50]. The IR spectra of 4a and 4b exhibited characteristic
v(CO) stretching vibrations at wavenumbers lower than those of
3a and 3b by ca. 21 cmꢀ1, which is due to the enhanced back-dona-
tion of metal to carbon as a result of the electron rich C5(CH3)5 li-
gand. A characteristic band due to CN stretching of HMTA was
observed at 1227–1244 cmꢀ1 as expected [51]. The v(CO) vibra-
tions of the mononuclear complexes were not significantly differ-
ent from those of the dinuclear complexes and therefore it was
not possible to distinguish the mononuclear from the dinuclear
g
g
ylimidazole), which is a part of an on-going study on functional-
ized transition metal alkyl complexes [41–48].
2. Results and discussion
The three N-heterocyclic ligands employed in this investigation
react with the ether complexes [Cp(CO)2Fe(OEt2)]BF4 (1) and
[Cp⁄(CO)2Fe(THF)]BF4 (2) at room temperature in dichloromethane
to afford complexes 3–8 as shown in Scheme 1. The N-heterocyclic
ligands are generally good electron donors and therefore readily
displace weakly bound Et2O and THF molecules. All the complexes
were obtained in moderate to excellent yields as yellow to orange
solids, except for compound 6c which was obtained in a low yield.
They are fairly stable in air but slowly decompose when in solution
and particularly when exposed to light. For this reason, manipula-
tions of the compounds in solution were done in the dark under
strictly anaerobic conditions. The complexes have been fully
characterized by elemental analysis, NMR and IR spectroscopy
R
R
R
R
R
R
R
R
L
R
R
R
R
L
CO
CO
R
R
R
R
L
R
R
L
E
L
R
+Fe
+Fe
R
+Fe
R
+
+Fe
Fe
+
CH2Cl2
OC
CH2Cl2
OC
OC
R
OC
R
CO
24 °C
CO
24 °C
CO
CO
R
R
Mononuclear complexes
Ether complexes
Dinuclear complexes
Mononuclear complexes
R
L
R
E
R
L
R
H
L
7 H
1-meIm
1-meIm
1
2
H
Et2O
THF
3b H
HMTA
HMTA
DABCO
DABCO
3a
HMTA
HMTA
8
CH3
CH3
4b
CH3
4a CH3
6b H
6a
H
DABCO
6c CH3
Scheme 1. Reactions of etherate complexes 1 and 2 with N-heterocyclic ligands.

C.M. M’thiruaine et al. / Inorganica Chimica Acta 390 (2012) 83–94
85
complexes based solely on carbonyl vibration frequency. However,
the IR spectra of the mononuclear complexes exhibited bands in
the fingerprint region which were significantly different from
those of the dinuclear complexes. For example, the IR spectrum
of dinuclear complex 3a show peaks at 918, 847, 712, 646 and
473 cmꢀ1 which were absent in the IR spectrum of mononuclear
complex 3b. On the other hand 3b exhibited peaks at 824, 655,
530 and 390 cmꢀ1 which were missing in the IR spectrum of 3a.
Coordination of HMTA to the metal decreases molecular sym-
metry resulting in a highly complex 1H NMR spectrum with a
multiple spin system making the assignment of the methylene
protons difficult. Hence the literature NMR data for the coordi-
nated HMTA or its derivative 1,3,5-triaza-7-phosphaadamantane
(PTA) are often reported as a range [1,4,7,52], and a similar strat-
egy is adopted for this study. The proton NMR spectrum of 3a in
acetonitrile-d3 consists of a sharp singlet at 5.42 ppm integrating
for 10 protons, assignable to two identical cyclopentadienyl
ligands, while the Cp⁄ analogue, compound 4a, exhibited a reso-
nance peak integrating for 30 protons and assignable to the two
identical pentamethylcyclopentadienyl protons at 1.86 ppm.
Multiple resonance peaks assignable to the 12 protons of the
methylenes bridging the nitrogen atoms of the HMTA ligand in
the dinuclear complexes 3a and 4a are observed in the range
4.16–4.50 ppm.
NMR spectrum of compound 4b indicating a decrease in
r
acidity
of the metal fragment upon changing from Cp to Cp⁄ which con-
forms with the expected enhanced
p
-back donation in Cp⁄ com-
plexes [54]. The peak corresponding to less deshielded
methylene carbons C4, C6, and C10 bridging the uncoordinated
nitrogen atoms were observed at 71.1 and 71.2 ppm for com-
pounds 3b and 4b, respectively, implying that the effect of chang-
ing the Cp to Cp⁄ was insignificant on these methylene groups.
Complex 4b reacted with 1 at room temperature by displacing
the {Cp⁄(CO)2Fe} fragment to give a mixture of compounds 3a,
3b, and [Cp⁄(CO)2Fe]2 rather than the expected mixed ligand com-
plex [{Cp(CO)2Fe}(l
-HMTA){Fe(CO)2Cp⁄}](BF4)2. There was no evi-
dence indicating formation of the mixed ligand complex at room
temperature. This was probably due to the high electrophilic
nature of the {Cp(CO)2Fe} group which rapidly reacted by displac-
ing the relatively less electrophilic {Cp⁄(CO)2Fe} group at room
temperature. However, when the reaction was repeated and main-
tained at 0 °C for 1 h the compound [{Cp(CO)2Fe}(l-HMTA){Fe(CO)2
Cp⁄}](BF4)2 was obtained as an air-sensitive orange solid which
was characterized by NMR spectroscopy.
In another attempt to prepare the mixed ligand complexes, a
mixture of a solution of 3b in acetonitrile and compound 2 in
dichloromethane were stirred at room temperature for 3 h after
which the starting material 3b precipitated out as a yellow residue.
The acetonitrile complex [Cp⁄(CO)2Fe(NCMe)]BF4 was obtained in
98% yield (based on compound 2) from the filtrate by precipitation
using diethyl ether. The molecular structure, physical and spectro-
scopic data of [Cp⁄(CO)2Fe(NCMe)]BF4 are reported elsewhere [55].
Thus, the {Cp⁄(CO)2Fe} group has preferential binding affinity for
NCMe when compared to the coordinated HMTA. It should be
noted that based on Pearson’s rule on hard and soft acids and bases
the preferential binding of the {Cp⁄(CO)2Fe} group to acetonitrile
does not in any way contradict the formation of the bridged com-
plex 4b, since the soft acid will interact more strongly with a soft
base than a hard base. Generally, metal centres that are electron
rich will interact weakly with strong electron-donating ligands.
This leads to weak M–L bonding and ease of ligand dissociation.
The strong interaction of iron-acetonitrile in [Cp⁄(CO)2Fe
(NCCH3)]BF4 is confirmed by a shorter Fe–N bond (1.924 Å) [55].
To ascertain the water-stability of the reported complexes, the
NMR data of the dinuclear HMTA complex 3a and the mononuclear
complex 4b were also collected in D2O. These data are given in the
Experimental Section. Both the 1H and 13C NMR spectra did not
show any evidence of decomposition. Peaks remained sharp even
after allowing the solution to stand for 10 h.
The 1H NMR spectra of the mononuclear complexes 3b and 4b
show three resonance peaks each; a singlet peak integrating for 6
protons, assignable to methylene protons adjacent to coordinated
nitrogen, and a set of two broad resonance peaks, integrating for
3 protons, each assignable to axial and equatorial protons of meth-
ylenes bridging the uncoordinated nitrogen. Similar observations
were made by Darensbourg and Daigle in the 1H NMR spectrum
of Mo(CO)5(HMTA) recorded in acetone [53].
In the 13C{1H} NMR spectra of the dinuclear complexes 3a and
4a (Fig. 1a), a peak corresponding to C2 is observed at ca.
86.6 ppm, shifted downfield as a result of the deshielding effect
of the two metal centres. The peak assignable to the less deshield-
ed C6 is observed upfield relative to other methylene carbons at ca.
73 ppm, while the peak corresponding to the four identical meth-
ylene carbons C4, C8, C9 and C10 appears at ca. 81.0 ppm. Unlike
the dinuclear complexes, the 13C{1H} NMR spectra of the mononu-
clear complexes 3b and 4b showed two peaks for the bridging
methylene carbons of the coordinated HMTA ligand; one peak cor-
responding to the three equivalent methylene carbons closer to the
coordinated nitrogen and the other peak corresponding to the
three equivalent methylenes bridging the uncoordinated nitrogen
atoms. The 13C{1H} NMR spectrum of 3b shows a singlet at
83.5 ppm corresponding to the methylene carbons C2, C8 and C9
Furthermore, the mass spectroscopy data of compounds 3a and
4b collected in 100% water confirmed the stability of these
compounds in water. The mass spectrum of 4b show a base
peak at m/z 329 which corresponds to the molecular ion
(Fig. 1b), while
a singlet corresponding to the equivalent
methylene carbons was observed at 81.8 ppm in the 13C{1H}
R
+
2+
R
R
R
R
R
R
R
R
R
R
R
C2
N7
Fe
R
R
Fe
N3
N1
C8
C2
N7
OC
R
Fe
N3
CO
CO
C4
N1
C8
OC
C10
OC
C9
C4
C10
OC
N5
C9
N5
C6
C6
3b
R = H
3a
R = H
4b
R = CH3
4a R = CH3
Fig. 1. Atomic numbering scheme of HMTA in dinuclear (a) and mononuclear (b).

86
C.M. M’thiruaine et al. / Inorganica Chimica Acta 390 (2012) 83–94
Table 1
Selected bond lengths (Å) and angles (°) for [{Cp(CO)2Fe}2(
l
-HMTA)](BF4)2 (3a).
Angle (°)
Bond
Length (Å)
Bonds
C(8)–N(2)
C(8)–N(1)
C(9)–N(3)
C(9)–N(1)
C(10)–N(4)
C(10)–N(1)
C(13)–N(4)
C(13)–N(3)
N(1)–Fe(1)
N(2)–Fe(2)
1.506(3)
1.506(3)
1.456(3)
1.516(3)
1.451(3)
1.510(3)
1.469(3)
1.475(3)
2.0858(18)
2.0817(17)
N(2)–C(8)–N(1)
N(4)–C(10)–N(1)
C(10)–N(1)–C(9)
C(12)–N(2)–C(11)
C(12)–N(4)–C(10)
C(12)–N(4)–C(13)
C(10)–N(4)–C(13)
C(6)–Fe(1)–C(7)
C(6)–Fe(1)–N(1)
C(7)–Fe(1)–N(1)
112.77(16)
112.35(17)
107.11(16)
106.38(16)
110.07(17)
109.46(19)
109.06(17)
93.01(11)
94.48(9)
95.27(9)
[Cp⁄(CO)2Fe(HMTA)]+ while that of 3a show a peak of weak
,
intensity at m/z 317 corresponding to the [Cp(CO)2Fe(HMTA)]+
fragment. The mass spectra of both compound exhibited frag-
mentation patterns which mainly involve loss of subsequent
carbonyl groups. The full mass spectroscopy data is given in the
Experimental Section.
Fig. 3. Crystal packing of compound 3a viewed down the b-axis.
2.1.1. Structural analysis of [{Cp(CO)2Fe}2(
The single-crystal X-ray diffraction study reveals that
[{Cp(CO)2Fe}2( -HMTA)](BF4)2 crystallizes in the orthorhombic
l-HMTA)](BF4)2
C–N bonds (1.476 Å) reported for the uncoordinated HMTA struc-
ture [56]. The difference in bond lengths can be attributed to loss
of symmetry upon coordination to the electrophilic iron centre.
Similar observations were reported by Hanic and Šubrtová in the
structural study of C6H12N4ꢁBH3 [57] and by Frost et al. in the struc-
tural study of PTAꢁBH3 [58]. For nitrogen coordinated PTA com-
plexes, elongation of (N)C-N mainly results from alkylation or
protonation of PTA, while metallation of PTA results in little or
no change in (N)C–N distance [59]. Other selected bond distances
and angles of 3a are listed in Table 1. The ORTEP diagrams showing
the atomic numbering scheme and the packing of the molecules in
the crystal are shown in Figs. 2 and 3, respectively. Crystallo-
graphic and refinement data are given in Table 2.
l
P212121 space group with one dicationic molecule and two coun-
ter-anions in the asymmetric unit. The two {Cp(CO)2Fe} units are
linked by the HMTA ligand through the nitrogen atoms in which
the coordination geometry around Fe can be described as distorted
octahedral with three sites occupied by a cyclopentadienyl ligand,
while the two carbonyls and the HMTA ligand occupy the remain-
ing three sites. The Fe–N bond distances were found to be
2.0817(17) and 2.0858(18) Å, which are comparable to the
2.092(4) Å in [(CO)4Fe(DABCO) [30], but longer than the Fe–N bond
lengths previously reported for cyclopentadienylirondicarbonyl
amine complexes [44,48,50]. The three carbon atoms adjacent to
the iron centre form a base with a distorted tetragonal geometry
about nitrogen with N–C bonds in the range 1.514 0.010 Å.
Valence angles are: Fe–N–C, 111.89 1.51° and C–N–C,
106.94 0.84°. The length of the remaining C–N bonds in the
molecule fall in the range 1.458 0.017 Å, unlike the equivalent
2.2. Reaction of 3b and 4b with NaBPh4
The reaction of mononuclear complexes 3b and 4b with NaBPh4
in acetone proceeds smoothly at room temperature with counter-
Fig. 2. The molecular structure of 3a showing atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level with H atoms presented as small
spheres.

C.M. M’thiruaine et al. / Inorganica Chimica Acta 390 (2012) 83–94
87
Table 2
Crystal data and structure refinement data for [{Cp(CO)2Fe}2(
l
-HMTA)](BF4)2 (3a), [Cp(CO)2Fe(1-meIm)]BF4 (7) and [Cp⁄(CO)2Fe(1-meIm)]BF4 (8).
Compound
3a
20H22B2F8Fe2N4O4
667.74
173(2)
0.71073
orthorhombic
P212121
7
8
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimension
a (Å)
C
C11H11BF4FeN2O2
345.88
173(2)
0.71073
monoclinic
P21/c
C16H21BF4FeN2O2
416.01
173(2)
0.71073
orthorhombic
Pna21
8.60250(10)
10.2951(2)
27.5041(4)
90
17.8135(6)
9.9651(4)
23.9093(10)
90
17.0840(4)
13.9877(4)
7.6884(2)
90
b (Å)
c (Å)
a
(°)
b (°)
90
90
95.3860(10)
90
4225.5
12
1.631
90
90
c
(°)
Volume (Å3)
2435.86(7)
4
1.821
1.29
1344
1839.65(8)
4
1.502
0.871
856
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
)
1.119
2088
Crystal size (mm)
Crystal description
Crystal colour
Theta range for data collection
Index ranges
0.47 ꢂ 0.46 ꢂ 0.16
0.44 ꢂ 0.41 ꢂ 0.13
0.44 ꢂ 0.40 ꢂ 0.01
plate
plate
prism
brown
1.48–27.99°.
yellow
1.15–28.00
yellow
1.88–28.00
h
k
l
ꢀ11 ? 11
ꢀ23 ? 15
ꢀ22 ? 21
ꢀ13 ? 13
ꢀ13 ? 9
ꢀ18 ? 18
ꢀ36 ? 36
ꢀ31 ? 31
ꢀ10 ? 10
Reflections collected
Independent reflections
Internal fit
33919
28785
20793
5902
R(int) = 0.0418
integration
0.5823; 0.8202
full-matrix least-squares on F2
361
10195
R(int) = 0.0355
integration
0.6388; 0.8682
full-matrix least-squares on F2
571
4441
R(int) = 0.0465
integration
0.7006; 0.9913
full-matrix least-squares on F2
241
Absorption correction
Transmission factor (TMin; TMax
Refinement method
Parameters
)
Goodness-of-fit (GOF) on F2
1.051
1.046
1.038
Final R indices [I > 2
r
(I)]
R1 = 0.0284, wR2 = 0.0705
R1 = 0.0314, wR2 = 0.0715
0.683 and ꢀ0.473
R1 = 0.0535, wR2 = 0.1456
R1 = 0.0787, wR2 = 0.1663
1.604 and ꢀ0.943
R1 = 0.0342, wR2 = 0.0836
R1 = 0.0418, wR2 = 0.0870
0.400 and ꢀ0.312
R indices (all data)
Largest difference in peak and hole (e Åꢀ3
)
anion exchange to provide complexes [Cp(CO)2Fe(HMTA)]BPh4
(5a) and [Cp⁄(CO)2Fe(HMTA)]BPh4 (5b), respectively. These com-
plexes were obtained in high yields as yellow microcrystalline sol-
ids by precipitation using diethyl ether from their CH2Cl2 solutions.
[Cp⁄(CO)2Fe(DABCO)]BF4 (6c), which was obtained as a yellow so-
lid in low yield by addition of diethyl ether into its solution in
CH2Cl2. The failure to form the dinuclear complex by [Cp⁄(CO)2Fe
(THF)]BF4 can be attributed to the high steric demand of both the
Cp⁄(CO)2Fe moiety and the ligand itself. Unlike HMTA, which has
a Tolman’s cone angle of 118° [60], DABCO has a Tolman’s cone an-
gle of ca. 132° [61] implying that, once one of its nitrogens is bound
to the metal centre, the other nitrogen becomes sterically crowded
thus preventing the coordination of the second Cp⁄(CO)2Fe moiety.
Complex 6a is an air stable orange solid which decomposes
without melting at temperatures above 174 °C. It is insoluble in
chlorinated solvents and hexane but soluble in water, acetone
and acetonitrile. The infrared spectrum of complex 6a exhibited
two bands at 2053 and 2000 cmꢀ1 assigned to the v(CO) of the
two equivalent [Cp(CO)2Fe]+ fragments. Moreover, the 1H NMR
spectrum of compound 6a in D2O exhibited a singlet at 3.01 ppm
assignable to the 12 protons of six equivalent N–CH2–N groups
and presenting a slight downfield shift relative to the N–CH2–N
of free uncoordinated DABCO by 0.34 ppm. A singlet attributed to
ꢀ
The bulky BPh4 anion renders the cationic complexes soluble in
dichloromethane and relatively more soluble in acetone and aceto-
nitrile. It also stabilizes the cations in solution and consequently
improves the resolution of their NMR spectra. For example, the
1H NMR spectra of 5a and 5b exhibited two doublets correspond-
ing to the axial and equatorial protons of the methylene groups
bridging the uncoordinated nitrogen atoms which were observed
as broad peaks in the 1H NMR spectra of 3b and 4b.
2.3. Reaction of 1 and 2 with DABCO
1,4-Diazabicyclo[2.2.2]octane (DABCO) reacts with one equiva-
lent of the ether complex (1) at room temperature to give a mix-
ture of the dinuclear complex [{Cp(CO)2Fe}2(l-DABCO)](BF4)2
(6a) and mononuclear complex [Cp(CO)2Fe(DABCO)]BF4 (6b) in a
9:10 ratio. The reaction of DABCO with two equivalents of com-
pound 1 also gave a mixture of 6a and 6b, however, the amount
of 6a in the mixture increased as the amount of compound 1 used
in the reaction is increased. The dinuclear complex 6a formed as an
orange precipitate after six hours of reaction and was easily sepa-
rated by filtration under nitrogen. The mononuclear complex re-
mained in solution and was obtained as a yellow solid by
precipitation using diethyl ether. The reaction of DABCO with three
equivalents of 1 afforded only the dinuclear complex 6a. In con-
trast, the reaction of DABCO with one to three equivalents of the
THF complex (2) gave only the mononuclear complex
10 protons of the two identical
g
5-cyclopentadienyl groups ap-
peared at 5.28 ppm. Its 13C{1H} NMR spectrum shows three sing-
lets at 58.5, 86.6 and 210.0 ppm assignable to the six identical
carbons of the methylene groups, 10 identical carbons of the two
g
5-cyclopentadienyl ligands and four identical carbons of the car-
bonyl groups, respectively, confirming the molecular symmetry of
the DABCO bridging the two [Cp(CO)2Fe]+ fragments. The peak
corresponding to methylene carbons of the ligated DABCO also
appears downfield relative to the non complexed DABCO
ligand (46.7 ppm). This downfield shift can be attributed to the
deshielding effect upon the coordination of the DABCO to the elec-

88
C.M. M’thiruaine et al. / Inorganica Chimica Acta 390 (2012) 83–94
Similarly, the 1H NMR spectrum of 6c obtained in CD3CN shows
C
6
peaks corresponding to the two sets of methylene protons at 3.33
and 3.18 ppm. The 13C{1H} NMR spectrum shows two peaks at 56.4
and 44.2 ppm corresponding to carbons bonded to the coordinated
nitrogen and those bonded to the uncoordinated nitrogen,
respectively.
N
3
C
4
N1 = pyridine nitrogen
N3 = pyrrole nitrogen
C
2
2.4. Reaction of 1-methylimidazole (1-meIm) with 1 and 2
C
Treatment of the etherate complexes 1 and 2 with a slight ex-
cess of 1-methylimidazole (1-meIm) in dichloromethane at room
temperature furnished the novel iron 1-methylimidazole com-
5
N
1
Fig. 4. Diagram of 1-methylimidazole showing the ‘pyridine and pyrrole nitrogens’.
plexes [(
in high yields. These complexes and the dimeric iron complexes
[(
5-C5R5)(CO)2Fe]2 were the only products detected in the reac-
g
5-C5R5)(CO)2Fe(1-meIm)]BF4 (R = H, 7; and R = CH3, 8)
trophilic metal centre. These NMR data are in agreement with
those reported by Matos and Verkade in their NMR elucidation of
the complex [{(CO)4Fe}2(l-DABCO)] [30].
g
tion mixture. The 1-methylimidazole complexes 7 and 8 were ob-
tained as yellow microcrystalline solids by precipitation from their
solutions using diethyl ether. Compound 8 exhibited higher stabil-
ity relative to 7 towards light, air and heat. For instance, the melt-
ing point of 8 is significantly higher than that of 7 by ca. 100 °C and
it was stable in air and exposure to light for several hours in the
solid state with minimal degradation. In contrast, compound 7 de-
graded within 2 h when it was subjected to similar conditions.
However, these complexes can be preserved for long periods of
time when sealed under nitrogen and kept in the dark at temper-
atures below 0 °C. The stability of Cp⁄ complexes is generally en-
hanced by the more electron-releasing Cp⁄ ligand. The infrared
spectra of compounds 7 and 8 show two strong CO stretching
bands as expected. The v(CO) of 8 were as expected lower by ca.
13 cmꢀ1 as compared to those of 7.
The mononuclear complexes 6b and 6c are moderately air sta-
ble and are soluble in water, dichloromethane, acetone and aceto-
nitrile. Each show two strong v(CO) stretching bands, with those of
6c appearing at lower wavenumbers due to the high electron den-
sity at the metal centre. The 1H NMR spectra of 6b and 6c exhibit
two broad peaks assigned to the two sets of methylene protons.
The 1H NMR spectrum of 6b obtained in D2O shows a peak corre-
sponding to the six protons of the methylene closer to the coordi-
nated nitrogen at 3.21 ppm, while the peak due to the six protons
of the methylenes in the neighbourhood of the uncoordinated
nitrogen appeared at 2.84 ppm. Its 13C{1H} NMR spectrum shows
two peaks at 58.3 and 46.0 ppm corresponding to carbons bonded
to the coordinated nitrogen and those bonded to uncoordinated
nitrogen, respectively. The assignment of these peaks was done
with the aid of heteronuclear NMR experiments and with compar-
ison of NMR data of the free DABCO ligand. The mass spectrum of
the mononuclear compound 6b recorded in 100% water, showed
peaks at m/z 289, 261 and 233 corresponding to [Cp(CO)2Fe(DAB-
CO)]+, [Cp(CO)Fe(DABCO)]+ and [CpFe(DABCO)]+, respectively, con-
firming the stability of the DABCO compounds in water.
Two medium absorption bands corresponding to C@C and C@N
stretching were observed at ca. 1531 and 1515 cmꢀ1, respectively,
indicating that the p-electrons of the ring were not involved in coor-
dination. The 1H NMR spectra of compounds 7 and 8 show three
peaks corresponding to the protons attached to the three different
sp2 hybridized carbons C2, C4 and C5 (Fig. 4) in the range between
6.89 and 7.90 ppm, which is the typical region for uncoordinated
Table 3
Selected bond lengths (Å) for compounds 7 and ꢀ.
7a
7b
7c
8
Bond
Length (Å)
Bond
Length (Å)
Bond
Length (Å)
Bond
Length (Å)
C(6)–O(1)
C(6)–Fe(1)
C(7)–O(2)
C(7)–Fe(1)
C(8)–C(9)
C(8)–N(1)
C(9)–N(2)
C(10)–N(1)
C(10)–N(2)
N(1)–Fe(1)
1.136(4)
1.787(4)
1.136(5)
1.789(4)
1.357(5)
1.385(5)
1.372(5)
1.326(4)
1.339(4)
1.973(3)
C(17)–O(3)
C(17)–Fe(2)
C(18)–O(4)
C(18)–Fe(2)
C(19)–C(20)
C(19)–N(3)
C(20)–N(4)
C(21)–N(3)
C(21)–N(4)
N(3)–Fe(2)
1.129(5)
1.787(4)
1.139(5)
1.788(4)
1.352(6)
1.376(5)
1.365(5)
1.318(4)
1.336(4)
1.977(3)
C(28)–O(5)
C(28)–Fe(3)
C(29)–O(6)
C(29)–Fe(3)
C(30)–C(31)
C(30)–N(5)
C(31)–N(6)
C(32)–N(5)
C(32)–N(6)
N(5)–Fe(3)
1.136(5)
1.788(4)
1.133(4)
1.789(4)
1.354(5)
1.380(4)
1.367(5)
1.328(4)
1.341(4)
1.980(3)
C(11)–O(1)
C(11)–Fe(1)
C(12)–O(2)
C(12)–Fe(1)
C(13)–N(1)
C(13)–N(2)
C(14)–C(15)
C(14)–N(1)
C(15)–N(2)
N(1)–Fe(1)
1.142(3)
1.778(3)
1.133(3)
1.787(3)
1.330(3)
1.347(3)
1.362(3)
1.385(3)
1.362(3)
1.9781(18)
Table 4
Selected bond angles (°) for compounds 7 and 8.
7a
7b
7c
8
Bonds
Angle (°)
Bonds
Angle (°)
Bonds
Angle (°)
Bonds
Angle (°)
N(1)–C(10)–N(2)
C(9)–C(8)–N(1)
C(8)–C(9)–N(2)
C(10)–N(1)–C(8)
C(10)–N(2)–C(9)
C(6)–Fe(1)–C(7)
C(6)–Fe(1)–N(1)
C(7)–Fe(1)–N(1)
111.0(3)
108.8(3)
106.6(3)
106.0(3)
107.6(3)
93.00(17)
93.27(14)
93.73(14)
N(3)–C(21)–N(4)
C(20)–C(19)–N(3)
C(19)–C(20)–N(4)
C(21)–N(3)–C(19)
C(21)–N(4)–C(20)
C(17)–Fe(2)–C(18)
C(17)–Fe(2)–N(3)
C(18)–Fe(2)–N(3)
110.7(3)
108.6(4)
106.7(3)
106.3(3)
107.6(3)
92.31(18)
93.09(14)
95.92(15)
N(5)–C(32)–N(6)
C(31)–C(30)–N(5)
C(30)–C(31)–N(6)
C(32)–N(5)–C(30)
C(32)–N(6)–C(31)
C(28)–Fe(3)–C(29)
C(28)–Fe(3)–N(5)
C(29)–Fe(3)–N(5)
110.2(3)
108.3(3)
107.0(3)
106.7(3)
107.7(3)
95.72(18)
91.11(14)
92.79(14)
N(1)–C(13)–N(2)
110.6(2)
108.9(2)
C(15)–C(14)–N(1)
C(14)–C(15)–N(2)
C(13)–N(1)–C(14)
C(13)–N(2)–C(15)
C(11)–Fe(1)–C(12)
C(11)–Fe(1)–N(1)
C(12)–Fe(1)–N(1)
106.71(19)
105.91(19)
107.88(19)
93.55(13)
94.72(10)
93.04(10)

C.M. M’thiruaine et al. / Inorganica Chimica Acta 390 (2012) 83–94
89
Fig. 5. The molecular structures of 7 (a) and 8 (b) showing atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level with H atoms presented
as small spheres.
olefins. This supports the IR data and is supported by the single crys-
tal X-ray diffraction data presented in Table 3. Peaks corresponding
to the protons attached to C5 and C2 appear at ca. 7.23 and 7.88 ppm,
respectively, which is a downfield shift of ca. 0.16 and 0.31 ppm rel-
ative to the uncoordinated 1-methylimidazole ligand. The coordina-
tion of the 1-methylimidazole is via the ‘pyridine nitrogen’ and this

90
C.M. M’thiruaine et al. / Inorganica Chimica Acta 390 (2012) 83–94
Fig. 6. (a) Crystal packing of 7 viewed down the b-axis. (b) Crystal packing of 8 viewed down the c-axis.
has the effect of deshielding the neighbouring carbons C5 and C2.
The effect appears to diminish across the ring, implying that the
delocalized p-electrons are not evenly distributed within the ring
Fe(C5H5N)]SbF6 [65] and falls within the range (1.958(5)–
1.999(2) Å) reported for iron imidazole complexes [36,66,67]. The
Fe–N bond (1.977 Å) in 7 is marginally shorter than the average
Fe–N bond (1.978 Å) in 8 (Table 3). This was expected because
the Cp⁄ ligand is known to increase electron density on the metal
centre which in this case leads to a weaker Fe–N bond in 8 relative
to that observed in the Cp analogue. 1-methylimidazole is planar
and lies on the same plane with Fe, with angles about the ‘pyridine
nitrogen’ adding up to ca. 360 °C. The 1-methylimidazole geometry
is similar to that of the coordinated 1-methylimidazole in
[Fe(TPP)(1-meIm)N3] [67] and bis(1-methylimidazole) complexes
of manganese [68].
Fig. 6a and b shows the packing of 7 and 8, respectively, in the
crystal lattice. The packing of 7 is characterized by an inversion
centre resulting in a head to head and tail to tail orientation of
the molecules in alternating layers. On the other handꢀin 8 discrete
cationic moieties are separated by alternating BF4 anions ar-
ranged in layers forming a zigzag pattern that are related by glide
planes perpendicular to the (0,1,0) and (1,0,0) axes and a 2-fold
screw axis along the z-axis.
of the coordinated 1-methylimidazole and hence the geometry of
the imidazole ring is slightly affected. This is clearly reflected in
the single crystal X-ray diffraction data presented in Table 3.
13C{1H} NMR spectra of compounds 7 and 8 show a slight downfield
shift of all peaks relative to the free 1-methyimidazole ligand with a
larger downfield shift observed for 7 than for 8. The NMR data of
compounds 7 and 8 collected in D2O were similar to those collected
in CD3OD and did not show any evidence of decomposition even
after 37 h. The mass spectrum of compound 8 collected in 100%
water showed a peak at m/z 329 corresponding to the molecular
ion [Cp⁄(CO)2Fe(1-meIm)]+, further confirming the stability of 1-
methylimidazole complexes in water.
2.5. Structural analysis of [(g
5-C5R5)(CO)2Fe(1-meIm)]BF4 (R = H, CH3)
(7 and 8)
For a more detailed understanding of the bonding of the 1-
methylimidazole (1-meIm) ligand, the molecular structures of
[Cp(CO)2Fe(1-meIm)]BF4 (7) and [Cp⁄(CO)2Fe(1-meIm)]BF4 (8)
were studied by single crystal X-ray crystallography. Selected bond
distances and angles are given in Tables 3 and 4, respectively. Crys-
tals of compound 7 were obtained as yellow plates that crystallized
in the monoclinic P21/c space group, with three independent
molecular cations and anions each in the asymmetric unit, while
compound 8 crystallized in the orthorhombic Pna21 space group
as yellow prisms, with one cation and a counterion in the asym-
metric unit. Crystal data and structure refinement information
for compounds 3a, 7 and 8, are summarized in Table 2. The 1-
3. Conclusion
The ether complexes, [(g
5-C5R5)(CO)2Fe(E)]BF4 (R = H; E = Et2O
and R = CH3, E = THF) have been shown to undergo nucleophilic
substitution with N-heterocyclic ligands such as hexamethylene-
tetramine (HMTA), 1,4-diazabicyclo[2.2.2]octane (DABCO) and 1-
methylimidazole (1-meIm) to form dinuclear and mononuclear
complexes of the types [{(
L = HMTA, DABCO; R = CH3; L = HMTA) and [(
g
5-C5R5)(CO)2Fe}2L](BF4)2 (R = H;
g
5-C5R5)(CO)2FeL]BF4
(L = HMTA, DABCO, 1-meIm), respectively. The more electrophilic
Cp containing metal fragment [Cp(CO)2Fe]+ displaced the Cp⁄ ana-
logue [Cp⁄(CO)2Fe]+ from its complex with HMTA when the reac-
tion was carried out at room temperature, but not when the
reaction was conducted at 0 °C. The reaction of the ethereal com-
methylimidazole ligand is
r-bonded to iron via the ‘pyridine nitro-
gen’ through the lone pair of electrons in the hybrid orbital. This
mode of bonding is thermodynamically favoured in order to retain
the aromaticity within the imidazole ring [62]. The coordination
about the iron is the familiar 3-legged piano-stool geometry
plexes with 1-methylimidazole gave complexes of the type [(g5
-
adopted by the [(
g
5-C5R5)(CO)2Fe(1-meIm]+ (Fig. 5a and b) with
C5R5)(CO)2Fe(1-meIm)]BF4 (R = H, CH3). The NMR, IR and single
crystal X-ray diffraction data of the compounds [Cp⁄(CO)2Fe(1-
meIm)]BF4 and [Cp(CO)2Fe(1-meIm)]BF4 show that the iron centre
has preferential binding affinity towards the ‘pyridine nitrogen’ of
the 1-methylimidazole ring resulting in a positive inductive effect
that makes the Fe–N bond in 1-methylimidazole complexes signif-
icantly shorter than the Fe–N bond in the dinuclear HMTA
complex.
mean bond angles around Fe involving the basal carbonyl and
imidazole ligands of about 90°.
The Fe–N bond lengths are between 1.973(3) and 1.9781(18) Å
as expected for iron-cyclic amine complexes [63–65]. These values
are close to Fe–N = 1.970(7) Å in the iron benzimidazole complex
[Cp(CO)2Fe(C7H6N2)]BPh4 [35], Fe–N = 1.983(28), 1.973(31) Å ob-
served in the two independent molecules of [Cp(CO)2-

C.M. M’thiruaine et al. / Inorganica Chimica Acta 390 (2012) 83–94
91
H, 4.15; N, 13.76%. 1H NMR (600 MHz, CD3CN): d 5.39 (s, 5H,
C5H5), 4.83 (br. s, 3H, axial), 4.46 (br s, 3H, equitorial), 4.60 (br, s
6H, CH2). 13C{1H} NMR (600 MHz, CD3CN): d 86.37 (C5H5), 83.49
(C2, C8, C9), 71.06 (C4, C6, C10), 209.79 (CO). IR (solid state):
4. Experimental
4.1. General
m
(CO) 2054, 2003 cmꢀ1. Decomposes at temperature >183 °C.
All manipulations were carried out under nitrogen atmosphere
using Schlenk line techniques. Nitrogen (Afrox) was dried over
phosphorus(V) oxide. Reagent grade THF, hexane and Et2O were
distilled from sodium/benzophenone and stored over sodium wire;
CH2Cl2 was distilled from phosphorus(V) oxide and used immedi-
ately. Acetone and MeCN were distilled from anhydrous CaCl2
and stored over type 4A molecular sieves. The other chemical re-
agents were obtained from the suppliers shown in parentheses:
dicyclopentadiene, 1,2,3,4,5-pentamethylcyclopentadiene, iron
pentacarbonyl, tetrafluoroboric acid diethyl ether, iodomethane,
mercury (Aldrich), silver tetrafluoroborate and DABCO (Merck),
HMTA (BDH), sodium (Fluka) and iodine (Unilab) were used as
supplied. Melting points were recorded on an Ernst Leitz Wetzlar
hot-stage microscope and are uncorrected. Elemental analyses
were performed on a LECO CHNS-932 elemental analyzer. Infrared
spectra were recorded using an ATR PerkinElmer Spectrum 100
spectrophotometer between 4000 and 400 cmꢀ1, in the solid state.
Mass spectra were recorded on an Agilent 1100 series LC/MSD trap
with an electrospray ionization (ESI) source and quadrupole ion
trap mass analyzer by direct infusion and ESI operated in the posi-
tive mode. Deionised water (100%) was used as mobile phase and
4.4. Preparation of [Cp(CO)2Fe(HMTA)]BPh4, 5a
Into a solution of [Cp(CO)2Fe(HMTA)]BF4 (0.120 g, 0.30 mmol)
in acetone (10 ml), a solution of NaBPh4 (0.180 g, 0.53 mmol) in
acetone (15 ml) was added and the mixture stirred for 4 h. The sol-
vent was removed under reduced pressure and the residue ex-
tracted with CH2Cl2 (15 ml). Diethyl ether was added to the
extract until the yellow precipitate had formed. The mixture was
allowed to stand for 20 min after which the mother liquor was syr-
inged off. The residue was washed with diethyl ether (2 ꢂ 5 ml)
and then dried under reduced pressure to give 0.17 g (90% yield)
of a yellow solid (5a). Anal. Calc. for C37H37BFeN4O2: C, 69.81; H,
5.82; N, 8.81. Found: C, 70.24; H, 5.26; N, 8.95%.1H NMR
(400 MHz, acetone-d6): d 5.69 (s, 5H, C5H5), 4.87 (s, 6H, (CH2)3),
4.74 (d, JHH = 12.29, 3H, axial CH), 4.56(d, JHH = 12.13, 3H, equato-
rial CH). 13C{1H} NMR (400 MHz, acetone-d6): d 87.89 (C5H5),
86.89 (C2, C8, C9), 72.47 (C4, C6, C10). IR (solid state):
m(CO)
2052, 2004 cmꢀ1. M.p., 138–139 °C.
4.5. Reaction of DABCO with one equivalent of [Cp(CO)2Fe(OEt2)]BF4
10 ll of the sample injected at a 0.3 ml/min flow rate. NMR spectra
were recorded on Bruker topspin 400 MHz and 600 MHz spectrom-
eters and the chemical shifts are reported in ppm. The deuterated
solvents, D2O (Aldrich, 99.9%), CDCl3 (Aldrich, 99.8%), acetone-d6
(Aldrich, 99.5%), and acetonitrile-d3 (Aldrich, 99.8%), were used as
purchased. The precursors [CpFe(CO)2(OEt2)]BF4 [44] and
[Cp⁄(CO)2Fe(THF)]BF4 [69] were prepared as previously reported.
A solution of complex 1 (0.940 g, 2.78 mmol) in CH2Cl2 (15 ml)
and DABCO (0.300 g, 2.68 mmol) in CH2Cl2 (10 ml) was stirred at
room temperature overnight after which a yellow precipitate
formed. This was filtered via a cannula and the residue washed with
CH2Cl2 (5 ꢂ 10 ml) to give 0.77 g (45% yield) of a yellow solid (6a).
Anal. Calc. for C20H22B2F8Fe2N2O4: C, 37.50; H, 3.44; N, 4.38. Found:
C, 37.29; H, 3.60; N, 4.67%. 1H NMR (400 MHz, CD3CN): d 5.33 (s, 5H,
C5H5), 3.00 (s, 12H, CH2), 13C{1H} NMR (400 MHz, CD3CN): d 86.70
(C5H5), 58.21 (CH2), 209.79 (CO). 1H NMR (600 MHz, D2O): d 5.28
(s, 5H, C5H5), 3.01 (s, 12H, CH2), 13C{1H} NMR (600 MHz, D2O): d
4.2. Preparation of [{Cp(CO)2Fe}2(l-HMTA)](BF4)2, 3a
A solution of HMTA (0.219 g, 1.56 mmol) in CH2Cl2 (20 ml) was
added to a solution of the ether complex 1 (2.200 g, 6.51 mmol) in
CH2Cl2 (20 ml) in a Schlenk tube and the mixture was stirred for
10 h under nitrogen at room temperature after which an orange
precipitate formed. The red mother liquor was syringed off and
the precipitate washed with portions of CH2Cl2 (5 ꢂ 10 ml), and
dried under reduced pressure resulting in an orange powdery solid
of 3a. Yield: 1.012 g, 97%. Anal. Calc. for C20H22B2F8Fe2N4O4: C,
35.93; H, 3.29; N, 8.38. Found: C, 36.03; H, 3.27; N, 8.22%. 1H
NMR (400 MHz, CD3CN): d 5.42 (s, 10H, C5H5), 4.16 (s, 2H, CH2),
4.38–4.47 (m, 8H, CH2), 4.50(s, 2H, CH2). 13C{1H} NMR (400 MHz,
CD3CN): d 86.37 (C5H5), 86.77 (C2), 80.17 (C4, C8, C9, C10), 68.47
(C6), 208.63 (CO). 1H NMR (600 MHz, D2O): d 5.47 (s, 10H, C5H5),
4.32–4.86 (m, 12H, CH2). 13C{1H} NMR (600 MHz, D2O): d 86.38
(C5H5), 86.72 (C2), 79.71 (C4, C8, C9, C10), 68.62 (C6), 208.94
(CO). Ms (ESI, water 100%, 350 °C) m/z (%) 317 (13) [Cp(CO)2-
86.63 (C5H5), 58.52 (CH2), 210.02 (CO). IR (solid state):
m(CO)
2053, 2000 cmꢀ1. Decomposes at temperature >174 °C.
The filtrate was treated as follows: diethyl ether was added and
the mixture allowed to stand for 2 h when a yellow precipitate
formed. The mother liquor was syringed off and the precipitate
washed with 3 ꢂ 10 ml of diethyl ether to give 0.54 g (52% yield)
of a yellow solid (6b). Anal. Calc. for C13H17BF4FeN2O2: C, 41.49;
H, 4.52; N, 7.45. Found: C, 41.98; H, 4.77; N, 7.37%. 1H NMR
(600 MHz, D2O): d 5.39 (s, 5H, C5H5), 3.14 (CH2), 2.84 (CH2).
13C{1H} NMR (600 MHz, D2O); d 86.75 (C5H5), 58.31 (CH2) 46.00
(CH2) 210.60 (CO). Ms (ESI, water 100%, 350 °C) m/z (%) 289 (21)
[Cp(CO)2Fe(DABCO)]+, 233 (100) [CpFe(DABCO)]+, 113 (15) [DAB-
CO + H]. IR (solid state): m .
(CO) 2050, 1996 cmꢀ1
4.6. Reaction of DABCO with three equivalent of [Cp(CO)2Fe(OEt2)]BF4
Fe(HMTA)]+, 261 (100) [CpFe(HMTA)]+. IR (solid state):
m(CO)
2058, 2009 cmꢀ1. Decomposes at temperature >196 °C.
A Schlenk tube was charged with a solution of complex 1
(1.921 g, 5.68 mmol) in CH2Cl2 (15 ml) and a solution of DABCO
(0.212 g, 1.89 mmol) in CH2Cl2 (10 ml) added. The mixture was
stirred for 6 h at room temperature after which an orange precip-
itate formed. The mother liquor was removed by filtration using a
cannula and the residue washed with CH2Cl2 (3 ꢂ 5 ml) and dried
under reduced pressure, resulting in an orange solid. The residue
was purified further by recrystallization from acetone/diethyl
ether and dried under reduced pressure to give a yellow solid of
6a. Yield: 0.860 g, 71%. Anal. Calc. for C20H22B2F8Fe2N2O4: C,
37.50; H, 3.44; N, 4.38. Found: C, 37.20; H, 3.23; N, 4.12%. 1H
NMR (400 MHz, CD3CN): d 5.33 (s, 5H, C5H5), 3.00 (s, 12H, CH2),
13C{1H} NMR (400 MHz, CD3CN): d 86.70 (C5H5), 58.21 (CH2),
0
4.3. Preparation of [Cp(CO)2Fe(HMTA)]BF4 , 3b
A Schlenk tube equipped with a magnetic stirrer was charged
with a solution of compound 1 (0.580 g, 1.72 mmol) in CH2Cl2
(10 ml) in the dark and a solution of HMTA (0.300 g, 2.14 mmol)
in CH2Cl2 (20 ml) added. The mixture was stirred at room temper-
ature for 16 h after which a yellow precipitate formed. The mixture
was then filtered through a cannula and the residue washed with
portions of CH2Cl2 (3 ꢂ 10 ml) and the residue dried under reduced
pressure to give a yellow solid of 3b. Yield: 0.65 g, 94%. Anal. Calc.
for C13H17BF4FeN4O2: C, 38.61; H, 4.21; N, 13.86. Found: C, 38.60;

92
C.M. M’thiruaine et al. / Inorganica Chimica Acta 390 (2012) 83–94
209.79 (CO). IR (solid state):
at temperature >174 °C.
m
(CO) 2053, 2000 cmꢀ1. Decomposes
and the rest of the procedure was executed as described in Sec-
tion 4.4 to give 0.11 g (82%) of compound 5b. Anal. Calc. for
42H47BFeN4O2: C, 71.39; H, 6.66; N, 7.93. Found: C, 70.72; H,
C
4.7. Preparation of [Cp⁄(CO)2Fe(DABCO)]BF4, 6c
6.70; N, 8.17%. 1H NMR (400 MHz, acetone-d6): d 2.01 (s, 15H,
C5(CH3)5), 4.68 (s, 6H, CH2), 4.60 (s, 3H, axial, CH), 4.57 (s, 3H, equa-
torial CH), 6.77 (br, 4H, p-CH), 6.92 (br, 8H, o-CH), 7.33 (br, 8H, m-
CH). 13C{1H} NMR (400 MHz, acetone-d6): d 10.02 (C5(CH3)5), 72.67
(C4, C6, C10), 83.29 (C2, C8, C9), 99.50 (C5(CH3)5), 122.22 (para-C,
Ph), 125.97 (meta-C, Ph), 130.90 (B-C)137.05 (ortho-C, Ph). IR (solid
A solution mixture of complex 2 (0.300 g, 0.74 mmol) in CH2Cl2
(15 ml) and DABCO (0.030 g, 0.27 mmol) in CH2Cl2 (10 ml) was
stirred at room temperature overnight. Diethyl ether (30 ml) was
added to the mixture and the mixture then allowed to stand undis-
turbed for 16 h at room temperature. A yellow microcrystalline so-
lid collected on the walls of Schlenk tube. The mother liquor was
syringed off, the crystals were washed with diethyl ether (2 x
5 ml) and dried under reduced pressure to give 0.03 g (25% yield)
of yellow solid, 6c. Anal. Calc. for C18H27BF4FeN2O2: C, 48.43; H,
6.05; N, 6.28. Found: C, 48.87; H, 6.14; N, 5.77%. 1H NMR
(400 MHz, CD3CN): d 2.01 (s, 15H, C5(CH3)5), 3.17 (t, JHH = 6.68 Hz,
6H, CH2), 3.34 (t, JHH = 6.74, 6H, (CH2)3). 13C{1H} NMR (400 MHz,
CD3CN): d 8.75 (C5(CH3)5), 44.17 (CH2), 51. 11 (CH2) 97.88
state): m
(CO) 2029, 1986 cmꢀ1. M.p., 149–150 °C.
4.11. Preparation of [Cp(CO)2Fe(1-meIm)]BF4, 7
1-Methylimidazole (0.40 ml, 5.04 mmol) was added to a solu-
tion of compound 1 (0.532 g, 1.57 mmol) in CH2Cl2 (10 ml) in a
Schlenk tube and the mixture stirred under nitrogen at room tem-
perature for 6 h. Into the resultant yellow-brown solution diethyl
ether was added until a yellow precipitate was formed. The precip-
itate was allowed to stand for 5 min after which the mother liquor
was syringed off and the yellow residue was washed with diethyl
ether (3 ꢂ 5 ml). Drying of the residue under reduced pressure
for 5 h gave 0.489 g (90%) of compound 7. Anal. Calc. for
(C5(CH3)5) 212.41 (CO). IR (solid state):
m .
(CO) 2021, 1969 cmꢀ1
4.8. Preparation of [{Cp⁄(CO)2Fe}2(
l
-HMTA)](BF4)2, 4a
A solution of HMTA (0.142 g, 1.01 mmol) in CH2CH2 (10 ml) was
added dropwise into a stirred solution of compound 2 (1.650 g,
4.06 mmol) in CH2Cl2 (10 ml) within 60 s. The mixture was stirred
under nitrogen at room temperature overnight and then filtered
into a pre-weighed Schlenk tube. Diethyl ether was added until
an orange precipitate formed and the mixture was allowed to
stand for 30 min, after which the mother liquor was syringed off.
The residue was washed with portions of diethyl ether
(3 ꢂ 10 ml) and dried under reduced pressure to give the orange
solid of 4a. Yield: 0.275 g, 34%. Anal. Calc. for C30H42B2F8Fe2N4O4:
C, 44.55; H, 5.20; N, 6.93. Found: C, 44.34; H, 5.35; N, 6.88%. 1H
NMR (400 MHz, CD3CN): d 1.86 (s, 30H, C5(CH3)5), 4.32–4.50 (m,
12H, (CH2)6), 13C{1H} NMR (400 MHz, CD3CN): d 8.93 (C5(CH3)5),
86.43 (C2), 81.90 (C4,C8, C9,C10), 78.42(C6), 98.45 (C5(CH3)5),
C11H11BF4FeN2O2: C, 38.15; H, 3.18; N, 8.09. Found: C, 37.90; H,
3.25; N, 8.16%. 1H NMR (400 MHz, MeOD): d 7.85 (s, 1H, CH),
7.19 (s, 1H, CH), 6.93 (s, 1H, CH), 5.38 (s, 5H, C5H5), 3.71 (s, 3H,
CH3), 13C{1H} NMR (400 MHz, MeOD): d 87.90 (C5H5), 36.08
(CH3), 125.19 (CH), 136.08 (CH), 209.79 (CO). 1H NMR (600 MHz,
D2O): d 7.70 (s, 1H, CH), 7.06 (s, 1H, CH), 6.86 (s, 1H, CH), 5.28 (s,
5H, C5H5), 3.62 (s, 3H, CH3), 13C{1H} NMR (600 MHz, D2O): d
86.35 (C5H5), 34.10 (CH3), 123.56 (CH), 134.62 (CH), 211.34 (CO).
IR (solid state): m
(CO) 2052, 2000 cmꢀ1. M.p., 48–50 °C.
4.12. Reaction of [Cp⁄(CO)2Fe(1-meIm)]BF4, 8
Into a solution of [Cp⁄(CO)2Fe(THF)]BF4 (0.370 g, 0.91 mmol) in
CH2Cl2 (15 ml) 1-methylimidazole (0.30 ml, 3.78 mmol) was added
and the mixture stirred in the dark for 8 h at room temperature.
After this period the reaction mixture changed colour from red to
yellow. It was then filtered into a pre-weighed Schlenk tube and
diethyl ether (30 ml) was added into the filtrate. The mixture
was allowed to stand for 10 min after which a bright yellow crys-
talline solid formed. The mother liquor was syringed off and the
residue was washed with portions of diethyl ether (2 ꢂ 10 ml),
and then dried under reduced pressure. Yield: 0.364 g, 96% of 8.
Anal. Calc. for C16H21BF4FeN2O2: C, 46.15; H, 5.04; N, 6.73. Found:
C, 46.11; H, 5.20; N, 6.65%. 1H NMR (400 MHz, CD3OD): d 1.78 (s,
15H, C5(CH3)5), 3.76 (s, 3H, N–CH3), 6.89 (s, 1H, @CH), 7.25 (s,
1H, @CH), 7.90 (s, 1H, @CH), 13C{1H} NMR (400 MHz, CDCl3): d
9.32 (C5(CH3)5), 35.12 (N-CH3), 98.36 (C5(CH3)5), 123.60 (@CH),
132.55 (@CH), 212.42 (CO). 1H NMR (400 MHz, D2O): d 1.68 (s,
15H, C5(CH3)5), 3.64 (s, 3H, N–CH3), 6.80 (s, 1H, @CH), 7.07 (s,
1H, @CH), 7.69 (s, 1H, @CH), 13C{1H} NMR (600 MHz, D2O): d
8.37 (C5(CH3)5), 34.02 (N–CH3), 98.38 (C5(CH3)5), 123.66 (@CH),
133.13 (@CH), 213.33 (CO). Ms (ESI, water 100%, 350 °C) m/z (%)
329 (30) [Cp⁄(CO)2Fe(1-meIm)]+, 305 (28) [Cp⁄(CO)Fe(1-
211.76 (CO). IR (solid state):
m
(CO) 2035, 1991 cmꢀ1
.
⁄
0
4.9. Preparation of [Cp (CO)2Fe(HMTA)]BF4 , 4b
A Schlenk tube was charged with a solution of compound 2
(0.633 g, 1.55 mmol) in CH2Cl2 (15 ml) and a solution of HMTA
(0.250 g, 1.79 mmol) in CH2Cl2 (20 ml) was added. The mixture
was stirred at room temperature under nitrogen for 18 h. The mix-
ture was then filtered through a cannula into a pre-weighed
Schlenk tube and diethyl ether was then added until a yellow pre-
cipitate formed. This was allowed to stand for 10 min after which
the mother liquor was removed by filtration and the yellow resi-
due washed with portions of CH2Cl2 (4 ꢂ 10 ml) and dried under
reduced pressure. Yield: 0.45 g, 61%. Anal. Calc. for C18H27BF4Fe-
N4O2: C, 45.57; H, 5.70; N, 11.81. Found: C, 46.01; H, 5.86; N,
11.74%. 1H NMR (400 MHz, CD3CN): d 1.83 (s, 15H, C5(CH3)5),
4.84 (br. s, 6H,(CH2)3), 4.49 (br, s, 6H, (CH2)3). 13C{1H} NMR
(400 MHz, CD3CN): d 8.39 (C5(CH3)5), 71.25 (C4, C6, C10), 81.84
(C2, C8, C9), 98.98 (C5(CH3)5). 210.51 (CO). 1H NMR (600 MHz,
D2O): d 1.85 (s, 15H, C5(CH3)5), 4.59 (br. s, 6H,(CH2)3), 4.53 (br, s,
6H, (CH2)3). 13C{1H} NMR (600 MHz, D2O): d 8.98 (C5(CH3)5),
71.72 (C4, C6, C10), 80.24 (C2, C8, C9), 98.75 (C5(CH3)5). 211.84
(CO). Ms(ESI, water 100%, 350 °C) m/z (%) 387 (100) [Cp⁄(CO)2-
Fe(HMTA)]+, 359 (12) [Cp⁄(CO)Fe(HMTA)]+, 331 (28) [Cp⁄Fe(HM-
meIm)+2H2]+, 273 (100) [Cp⁄Fe(1-meIm)]+. IR (solid state):
m(CO)
2041, 1986 cmꢀ1. M.p, 145–148 °C.
4.13. Reaction of [Cp⁄(CO)2Fe(HMTA)]BF4 with [Cp(CO)2Fe(OEt2)]BF4
in dichloromethane at room temperature
TA)]+. IR (solid state): (CO) 2031, 1982 cmꢀ1. M.p., 159–161 °C.
m
Into a stirred solution of [Cp⁄(CO)2Fe(HMTA)]BF4 (0.147 g,
0.31 mmol) in CH2Cl2 (10 ml), a solution of (1) (0.117 g, 0.35 mmol)
in CH2Cl2 (10 ml) was added within 3 min using a cannula. The
mixture was stirred overnight at room temperature after which
an orange solid stuck to the walls of the Schlenk tube. The mixture
4.10. Preparation of [Cp⁄(CO)2Fe(HMTA)]BPh4, 5b
The solution of 4b (0.090 g, 0.19 mmol) in acetone was treated
with a solution of NaBPh4 (0.100 g, 0.29 mmol) in acetone (15 ml)

C.M. M’thiruaine et al. / Inorganica Chimica Acta 390 (2012) 83–94
93
was filtered into a clean and dry Schlenk tube and the residue
Diagrams and publication material were generated using SHELXTL,
washed with CH2Cl2 (4 ꢂ 5 ml) to give 0.087 g of orange solid,
PLATON [73] and ORTEP-3 [74]. Table 2 summarizes crystal data and
structure refinement information while selected bond length and
angles are given in Tables 1, 3 and 4.
which by NMR and IR was found to be a mixture of [Cp(CO)2-
Fe(HMTA)]BF4 and [{Cp(CO)2Fe}2l-(HMTA)](BF4)2. Into the filtrate,
diethyl ether 30 ml was added and the mixture was allowed to
stand overnight. After this period no precipitate formed and there-
fore the solvent was removed under reduced pressure to give a
deep red oil which was found to be a mixture of decomposed Cp⁄
and Cp compounds as was suggested by the 1H NMR spectrum
which show numerous peaks in the Cp⁄ and Cp regions.
Acknowledgments
We sincerely thank the NRF, THRIP and UKZN (URF) for financial
support. The assistance of Dr. Manuel Fernandes (University of the
Witwatersrand) with the X-ray data collection and solution is
highly appreciated.
4.14. Reaction of [Cp⁄(CO)2Fe(HMTA)]BF4 with [Cp(CO)2Fe(OEt2)]BF4
in dichloromethane at 0 °C
Appendix A. Supplementary material
To a pre-cooled solution of [Cp⁄(CO)2Fe(HMTA)]BF4 (0.138 g,
0.29 mmol) in CH2Cl2 (10 ml) at ꢀ78 °C, a solution of [Cp(CO)2-
Fe(OEt2)]BF4 (0.102 g, 0.30 mmol) in CH2Cl2 (10 ml) was added
and the mixture allowed to warm to 0 °C. It was then stirred at this
temperature for 1 h after which an orange solid stuck on the walls
of Schlenk tube. The mixture was filtered and the residue washed
with CH2Cl2 portions until the washings were almost colourless.
The residue was then dried under reduced pressure to give
0.034 g of an air sensitive orange spongy solid of the dinuclear
CCDC 844986, 844987 and 844988 contains the supplementary
crystallographic data for compounds 3a, 7, and 8, respectively.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif. Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.ica.2012.04.003.
complex [{Cp(CO)2Fe}(l
-HMTA){Fe(CO)2Cp⁄}](BF4)2. 1H NMR
References
(400 MHz, CD3CN): 5.46 (s, 5H, C5H5), 4.63–4.4.23 (m, 12H, HMTA),
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8.38 (C5(CH3)5), 99.00 (C5(CH3)5).209.78, 208.62 (CO).
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